While microprocessors have found widespread application in computer installations which are directly monitored by the user, e.g. in installations having a user-operated terminal, an even more widespread application is in control and data processing installations using the microprocessor as part of so-called firmware in which the microprocessor is associated with a programmed storage or memory and responds to a variety of input signals to effect a variety of controlled functions depending upon the preprogrammed instructions.
Such circuitry can be used in energy supply installations, e.g. power plants, in industrial installations to control machinery or chemical processes, and the like.
Such systems are of particular advantage where decentralized control or local control is required or desired, i.e. where at a particular site in the plant, various measurement, control or regulatory signals are generated or arise and must be processed or monitored to perform or induce certain control functions. It is frequently impractical to transmit all of the monitored signals to a central location and return the various control function signals to the controlled location and hence microprocessor-controlled units may be provided at such locations to undertake many if not all of the required control functions.
Microprocessors have the advantage that they can perform tens of thousands of control functions or switching functions with a highly compact unit which can, by association with the programmable or read only memory, have an astonishingly wide variety of responses.
However, a disadvantage of microprocessor units in a decentralized or local application is that frequently a failure of the microprocessor remains unnoticed and not responded to for dangerously long periods which may be seriously detrimental in energy-producing or industrial installations. This is especially a problem because the highly complex nature of the microprocessor itself may obscure a failure.